(1) Field of the Invention
The present invention relates to systems and internal sensors for monitoring and quantifying ischemic damage in tissues.
(2) Description of the Prior Art
The gastrointestinal mucosa is at great risk of ischemia in the critically ill, and its disruption has been shown to be the motor of multiple organ failure, a leading cause of death. Knowledge of the level of damage can help guide therapy, reversing moderate damage and/or preventing further complications. For example, as indicated by path A in FIG. 6, the status of a healthy person's mucosa changes little, if at all, over time. Path C shows how the damage level of an ill person's ischemic mucosa greatly increases over the course of several hours if unchecked. However, as shown by path B, further damage can be arrested if the ischemic damage is detected and an appropriate course of treatment is undertaken. Unfortunately, there exists no clinically suitable method to directly monitor ischemic mucosal damage in the gastrointestinal tract of the critically ill patient.
Impedance spectroscopy has been used to detect ischemia (a condition of inadequate blood flow and oxygen delivery to a given tissue) in biological tissues using different instrumental methods. Impedance spectroscopy differs from other impedance measurements (which have long been used for a variety of biomedical applications such as cardiac output estimation, body fat measurement, and plethismography) in that it involves multiple measurements over a range of frequencies that as a whole contain significantly more information of the structural and electrical properties of the sample. For example, U.S. Pat. No. 5,454,377 to Dzwoczyk et al. teaches the assessment of ischemia in the myocardium, U.S. Pat. No. 5,807,272 to Kun et al. teaches the assessment of ischemia in directly accessible tissues (surface or subjacent tissue), and U.S. Pat. No. 6,055,452 to Pearlman shows the general characterization of the status and properties of tissues. However, none of these references show or describe a clinically acceptable method for impedance spectroscopy measurements of the inner wall of hollow viscous organs such as the gastrointestinal mucosa, in vivo or in situ.
On the other hand, several other methods have been devised to detect and/or monitor gastrointestinal ischemia using different measurement technologies. These include tonometry (as shown in U.S. Pat. Nos. 5,788,631 and 6,010,453 to Fiddian-Green), direct in situ measurement using an electrochemical sensor (as shown in U.S. Pat. No. 5,158,083 to Sacristan), and direct in situ measurement using an optochemical sensor (as shown in U.S. Pat. No. 5,423,320 to Salzman et al.) Additionally, U.S. Pat. No. 5,771,894 to Richards et al. shows external, non-invasive measurement using a magnetometer.
Numerous gastrointestinal catheter combinations, using electrodes or other sensors, have been used over the years for various measurements and medical applications. For example, U.S. Pat. No. 5,657,759 to Essen-Moller discloses a gastrointestinal output catheter, U.S. Pat. Nos. 5,848,965 and 5,438,985, both to Essen-Moller, show a gastric pH sensor/catheter combination, and U.S. Pat. No. 5,477,854 to Essen-Moller discloses a helicobaterpylori gastric infection sensor. Furthermore, U.S. Pat. No. 5,833,625 to Essen-Moller shows a gastric reflux monitor, U.S. Pat. No. 6,010,453 to Fiddian-Green shows a pressure nasogastric sump and tonometer combination, U.S. Pat. No. 5,158,083 to Sacristan et al. discloses a miniature pCO.sub.2 probe and catheter, and U.S. Pat. No. 5,423,320 to Salzman et al. shows an air tonometry sensor and catheter.
Several therapies have been proposed to limit or reverse the gastrointestinal mucosal damage and/or the associated complications in critical patients, including, for example, aggressive hemodynamic resuscitation (as shown in Gutierrez et al.), NO synthase modulators (as shown in U.S. Pat. No. 5,585,402 to Moncada et al.), rBPI protein (as shown in U.S. Pat. No. 6,017,881 to Ammons et al.), oral glutamine (as shown in U.S. Pat. No. 5,981,590 to Panigrahi et al.), and DHEA (as shown in U.S. Pat. No. 5,922,701 to Araneo). All of these can be optimally effective if they are administered within ideal treatment time windows depending on the status of the mucosa.
Accordingly, it is a primary object of the present invention to provide an impedance spectroscopy system, not only for detecting ischemia, but also for monitoring and quantifying ischemic mucosal damage, that is of great clinical value as a therapeutic guide for patients with intestinal ischemia and/or shock.
Another primary object of the present invention is to provide a catheter, for use with an impedance spectroscopy system, that is optimized for impedance spectroscopy in hollow viscous organs.
Yet another primary object of the present invention is to provide an impedance spectroscopy system and catheter for the continuous monitoring of the level of damage of the gastric mucosa in critically ill patients.